It is well known in the prior art to fabricate substantially cylindrical lightguide preforms from which lightguide fibers are drawn. One such technique is set forth in U.S. Pat. No. 3,737,292, wherein a preform is fabricated by using a flame hydrolysis process to deposit a plurality of coatings of doped glass particulate on the outside peripheral surface of a cylindrical starter rod. The starter rod is then removed and the resulting substantially hollow assembly is heated and drawn to reduce the cross-sectional area and to collapse the glass assembly to form a lightguide fiber having a solid cross-sectional area.
Such a technique is referred to as an "outside" deposition process and works well. However, undeposited particulate as well as the carrier gas pass into and contaminate the atmosphere. Additionally, other contaminants in the environment proximate the preform fabrication apparatus can deleteriously effect the deposition process, resulting in a preform which yields a high loss fiber.
Accordingly, there is a need for techniques whereby lightguide preforms can be fabricated in a substantially contaminant-free environment.